全文获取类型
收费全文 | 26783篇 |
免费 | 3091篇 |
国内免费 | 2426篇 |
专业分类
化学 | 2248篇 |
晶体学 | 30篇 |
力学 | 1901篇 |
综合类 | 531篇 |
数学 | 15844篇 |
物理学 | 6291篇 |
无线电 | 5455篇 |
出版年
2024年 | 44篇 |
2023年 | 262篇 |
2022年 | 405篇 |
2021年 | 488篇 |
2020年 | 559篇 |
2019年 | 560篇 |
2018年 | 617篇 |
2017年 | 816篇 |
2016年 | 894篇 |
2015年 | 725篇 |
2014年 | 1415篇 |
2013年 | 1781篇 |
2012年 | 1447篇 |
2011年 | 1713篇 |
2010年 | 1488篇 |
2009年 | 1750篇 |
2008年 | 1788篇 |
2007年 | 1871篇 |
2006年 | 1725篇 |
2005年 | 1624篇 |
2004年 | 1314篇 |
2003年 | 1245篇 |
2002年 | 1059篇 |
2001年 | 914篇 |
2000年 | 853篇 |
1999年 | 732篇 |
1998年 | 683篇 |
1997年 | 638篇 |
1996年 | 476篇 |
1995年 | 367篇 |
1994年 | 297篇 |
1993年 | 236篇 |
1992年 | 192篇 |
1991年 | 162篇 |
1990年 | 168篇 |
1989年 | 125篇 |
1988年 | 92篇 |
1987年 | 77篇 |
1986年 | 71篇 |
1985年 | 94篇 |
1984年 | 76篇 |
1983年 | 56篇 |
1982年 | 77篇 |
1981年 | 67篇 |
1980年 | 46篇 |
1979年 | 40篇 |
1978年 | 33篇 |
1977年 | 28篇 |
1976年 | 30篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Using recursive variants of Baire notions of nowhere dense and meagre sets we study the topological size of speedable and infinitely often speedable functions in a machine-independent framework. We show that the set of speedable functions is not “small” whereas the set of infinitely often speedable functions is “large”. In this way we offer partial answers to a question in [4]. 相似文献
12.
界面应力的正确评价是分析薄膜涂层材料力学特性的难题之一。利用镜像点法和Dirichlet等值性原理,本文推导了等厚双层薄膜涂层材料受表面集中力作用的平面问题理论解。该显式理论解是以固定在各镜像点上的局部坐标系下的Goursat应力函数的形式给出的。对应于高阶镜像点的应力函数,可通过递推的方法,从对应于低阶镜像点的应力函数求得,而且也易于计算机编程。随着镜像点阶数的增大,它与界面的距离也越来越大,因而相对应的应力函数对界面应力的影响越来越小。最后的算例表明,只需考虑前面有限个镜像点,便可获得足够精度的解。该理论解可作为格林函数,以求解复杂问题的理论解,也可用作边界元法的基本解,提高数值计算的精度和效率。 相似文献
13.
A fourth‐order compact finite difference scheme on the nine‐point 2D stencil is formulated for solving the steady‐state Navier–Stokes/Boussinesq equations for two‐dimensional, incompressible fluid flow and heat transfer using the stream function–vorticity formulation. The main feature of the new fourth‐order compact scheme is that it allows point‐successive overrelaxation (SOR) or point‐successive underrelaxation iteration for all Rayleigh numbers Ra of physical interest and all Prandtl numbers Pr attempted. Numerical solutions are obtained for the model problem of natural convection in a square cavity with benchmark solutions and compared with some of the accurate results available in the literature. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
14.
J. J. Rehr 《Foundations of Physics》2003,33(12):1735-1742
The Golden rule expression for x-ray absorption spectra (XAS) is typically calculated within a one-particle (quasiparticle) approximation and generally leads to good agreement between theory and experiment. The fact that a quasiparticle approximation works fairly well is surprising, since it neglects satellite excitations and intrinsic losses due to a suddenly created core-hole. The resolution of this paradox requires physics beyond the independent particle approximation. This is discussed here using an effective Green's function formulation based on a quasi-boson model that takes interference between inelastic losses into account. This approach shows that inelastic excitations such as multi-electron excitations tend to be suppressed, and that the XAS is given by a broadened quasiparticle particle approximation, together with weak satellite structure and edge singularity effects. 相似文献
15.
16.
S. A. Patlazhan 《Journal of Polymer Science.Polymer Physics》1993,31(12):1649-1665
A statistical theory of light scattering from deformed isotropic and textured heterogeneous polymer materials is formulated. Two types of textured structures are analyzed: assemblies of optically isotropic and anisotropic rods and a spatially anisotropic distribution of isotropic spherical inclusion centers. The small-angle Hv light-scattering patterns are calculated. The appearance of scattering from isotropic rods and spheres in deformed materials has been demonstrated. The changes of the Hv scattering patterns as a function of elongation and strucuture parameters are discussed. © 1993 John Wiley & Sons, Inc. 相似文献
17.
The complete proofs of Krein’s theorem on the spectral shift function and the trace formula are given for a pair of self-adjoint
operators such that either (i) their difference is trace-class or (ii) the difference of their resolvents is trace-class.
The proofs, essentially due to Krein, is based on Herglotz’s theorem on the boundary value of the analytic functions whose
imaginary part is non-negative on the upper half plane, and an almost optimal class of functions are obtained for which the
trace formula is valid. Also an alternative method based on Weyl-von Neumann’s theorem for self-adjoint operators, avoiding
the complex function theory and inspired by Voiculescu’s work, is given for the first case. Furthermore, some applications
of the spectral shift function have been discussed. 相似文献
18.
A. M. Stokolos 《Mathematical Notes》1998,64(5):646-657
It is proved that there exists an integrable function on [0, 1]2 whose integral is nondifferentiable in each direction belonging to a set everywhere dense in [0, 2π] but is strongly differentiable.
Translated fromMatematicheskie Zametki, Vol. 64, No. 5, pp. 749–762, November, 1998. 相似文献
19.
研究函数族的正规性定则是复变函数论中的一个重要且有意义的工作.引进多元K-拟全纯函数的定义,并给出了多元K-拟全纯函数族的一个正规定则. 相似文献
20.
详细介绍了在改进红外焊缝检测仪的过程中实时信号的一种抗干扰方法--自相关方法。重点离自相关方法的数学模型,软件框图及设计思想,并给出了实验结果。 相似文献